Ultratoughening of Biobased Polyamide 410

Abstract

The microstructural, thermomechanical, and quasistatic mechanical properties of biobased polyamide 410 (PA410)/poly(octane-co-ethylene)-g-maleic anhydride (POE-g-MA) blends with the impact toughener in the composition range of 0-20 wt % have been investigated, with an aim to overcome the poor notch and strain sensitivity of PA410. The crystallinity of the blends obtained from enthalpic measurements and initial degradation temperature indicating thermal stability remained mostly unaffected. A remarkably substantial increase, i.e., ∼15-fold enhancement, in the impact strength of the PA410/POE-g-MA blends leading to ultratoughening of PA410 accompanied by a significant increase in tensile strain at breaking is achieved though the elastic modulus (E) and yield strength (σ) decreased with impact modifier content. Thermomechanical analysis revealed a broadening in the loss tangent peak in the temperature range of ∼-50 to -30 °C corresponding to the POE phase, whereas the loss tangent peak corresponding to the PA410 phase stayed unaffected. Conventional theoretical models such as the rule of mixture and foam model were used to analyze the micromechanics of low-strain (<1%) mechanical response (E), and Nikolais-Narkis model and Isahi-Cohen models, for high-strain (>2%) mechanical response (σ). The interdependence of impact toughness, ductility ratio, and domain size of the dispersed rubber phase in the PA410/POE-g-MA blends could successfully be established vis-à-vis the mechanistic role of interparticle distance. Scanning electron microscopy showing domain coalescence of the soft elastomeric POE phase thus reiterated the pivotal role of interdomain distance and domain size in influencing the toughening mechanism of PA410/POE-g-MA blends. The qualitative phase distribution attributes based on atomic force microscopy remained in sync with quantitative parameters, such as domain size, hence reaffirming the mechanism behind ultratoughening of PA410 by POE.